The 79-year-old president told delegates to a crucial Communist Party summit that Cuban politicians and other important officials should be restricted to two, five-year terms.

Castro officially took over from his brother Fidel in 2008, meaning he would be at least 86 when his second term as Cuban leader ended, depending on how the law is written.

The proposal was made at the latter stage of a long speech in which the Cuban leader forcefully backed a list of economic changes which together represent a sea change for the country's socialist system, including the eventual elimination of the ration book and other subsidies, the decentralisation of the economy and a new reliance on supply and demand in some sectors.

But he drew a line in the Caribbean sand across which the reforms must never go, telling party luminaries that he had rejected dozens of suggested reforms which would have allowed the concentration of property in private hands.

Castro said the country had ignored its problems for too long, and made clear Cuba had to make tough decisions if it wanted to survive.

"No country or person can spend more than they have," he said. Two plus two is four. Never five, much less six or seven - as we have sometimes pretended," he said.

The Cuban leader alternated between reassurance that the economic changes were compatible with socialism, and a brutal assessment of what has not worked in the past.

Castro said the monthly ration book of basic foods, perhaps the most cherished of subsidies, represented an "unbearable burden ... and a disincentive for work."

Fidel Castro was not present for the speech, but a chair was left empty for him near his brother.